Preheat your oven to 350°F. Line an 8x8 baking dish with parchment paper and set it aside.
In a large mixing bowl, add the browned butter. To brown the butter, melt it in a saucepan over medium heat, stirring frequently, until it develops a nutty aroma and brown bits form.
Add the dark brown sugar, white sugar, and pumpkin puree to the browned butter. Whisk until the mixture is smooth and well combined.
Stir in the vanilla extract and eggs, whisking again until fully incorporated.
Add the dry ingredients—flour, baking powder, and pumpkin spice seasoning—into the wet mixture all at once.
Mix the wet and dry ingredients together until the batter is thick and smooth with no lumps.
Spread half of the batter evenly in the prepared baking dish.
Scoop dollops of marshmallow fluff onto the batter and use a spoon to spread it into an even layer.
Pour the remaining batter over the marshmallow layer, spreading it evenly to cover.
Bake the bars on the bottom rack for 55 minutes, or until a toothpick inserted into the pumpkin layer comes out with only moist crumbs.
Allow the bars to cool completely for about an hour before handling.
When ready to serve, melt the chocolate chips in the microwave, heating in 30-second intervals and stirring until smooth.
Drizzle the melted chocolate over the cooled Pumpkin S’mores Bars.
Slice into squares, serve, and enjoy!